Cds-chalcogen ternary compound mixture as photoconductive material in an electrophotographic member

ABSTRACT

AN ELECTROPHOTOGRAPHIC PHOTOSENSITIVE MEMBER WHICH COMPRISES A PHOTOCONDUCTIVE LAYER COMPRISING CDS AND A CHALCOGEN TERNARY COMPOUND OF THE FORMULA   X4YZ6   WHERE X IS ZN OR CD, Y IS SI OR GE AND Z IS S, SE OR TE.

Aug. 1, 1972 v HIROSHI HANADA 3,681,067

()dSCHAI|COGEN 'IERNAHY (JUMFOUND MIXTURE AS PHOTOCONDUCTIVE MATERIAL IN AN ELECTROPHOTOGRAPHIC MEMBER Filed Aug. 6, 1970 FIG. I

FIG. 2

RELATIVE PHOTO -CONDUCTIV|TY WAVELENGTH FIG. 3

RELATIVE PHOTO -CONDUCTIV|TY o 400 500 600 700 (ml) WAVELENGTH United States Patent U.S. c1. 961.5 3 Claims ABSTRACT OF THE DISCLOSURE An electrophotographic photosensitive member which comprises a photoconductive layer comprising CdS and a chalcogen ternary compound of the formula X,YZ

where X is Zn or Cd, Y is Si or Ge and Z is S, Se or Te.

This invention relates to an electrophotographic photosensitive member having a suflicient sensitivity over the entire visible light region and more particularly to an electrophotographic photosensitive member useful for duplicating colored originals.

There have hitherto been known many kinds of materials having photoconductive property. Among them, those belonging to cadmium chalcogan binary compounds are important because cadmium sulfide are now practically used and further cadmium selenide and a solid solution of cadmium sulfide and cadmium selenide are on their way to practice.

However, all these cadmium chalcogen binary com pounds have a drawback that the spectrum sensitivity is high at the long wavelength side of visible light region and low at the short wavelength side below 500 my. This characteristic is not favorable to color duplication. For example, the spectrum sensitivity of the photosensitive member using cadmium sulfide is as shown in FIG. 3.

To compensate this defect, zinc chalcogen binary compounds and zinc oxide have been investigated which have sensitivity to a short Wavelength region. However, since the zinc chalcogen binary compounds have a very low sensitivity and zinc oxide is accompanied by fatigue effect, neither of them is suitable for sensitivity compensa tion of cadmium chalcogen binary compounds.

Heretofore, there has been known a ternary compound having the formula where X is selected from the group consisting of Zn and Cd, Y is selected from the group consisting of Si and Ge, and Z is selected from the group consisting of S, Se and Te, which has a sensitivity over the wide wavelength region, i.e. from 300 to 500 m ranging from a short wavelength region of visible light to ultraviolet region. This compound has inherently such wide sensitivity region without incorporating any activating agent thereto.

Representative ternary compounds having the above formula are Cd SiS Cd SiSe Cd SiTe Cd GeS Cd GeSe Cd GeTe ZH4SIS5, Zn SiSe Zn SiTe Zn GeS Zn GeSe and Zn, GeTe However, these compounds have hitherto been used 3,681,067 Patented Aug. 1, 1972 only in a single crystal form or in a sintered form for producing photocells, and no attempt has been made to use them as materials for electrophotography in a vapor deposited film form or powder form. This may be due to the fact that these compounds are obtained in a porous spongy block form when they are prepared from CdS, ZnS, Si and S by heat treatment, and when these are vapor-deposited or ground, the deposited film or powder thus obtained has a low resistance and lacks in an ability to hold electrostatic charge required in electrophotography. Therefore, at present, photosensitive materials have not been found which are suited for color duplication.

As the result of basic experiments made on the abovementioned chalcogen ternary compounds, the present inventor has found that this lowering of resistance is mostly caused by disorder and strain of crystal and crystal lattice defect produced in the course of vapor deposition and grinding. He has also succeeded in removing these defects and imparting the said compounds a sufiicient resistance to be used as material for electrophotography, by applying appropriate heat treatment or chemical treatment to them. He has further succeeded in giving suflicient resistance to the solid solutions of them, solid solutions between them and the binary compounds, and matters activated by adding impurities.

The feature of this invention resides in that the photosensitive layer contains a photosensitive chalcogen ternary compound composed of cadmium or zinc, silicon or germanium, and chalcogen element, solid solution thereof, a cadmium chalcogen binary compound, or solid solution thereof which has been given a sufiicient resistance by the above-mention treatments.

A further feature of this invention resides in that the photosensitive member is obtained by laminating a layer containing a chalcogen ternary compound composed of cadmium or zinc, silicon or germanium, and chalcogen element or solid solution thereof with a layer containing a cadmium chalcogen compound or solid solution thereof, and these ternary and binary compounds having been given a sufiicient resistance by the above-mentioned treatments.

In other words, this invention relates to an electrophotographic photosensitive member characterized by having a photosensitive layer containing substances (I) and (II) as mentioned below, or laminating on a base two photosensitive layers each of which contains at least one of the substances (1) and (II) as mentioned below.

(I) At least one kind of photosensitive cadmium chalcogen binary compounds or their solid solutions.

(II) At least one kind of photosensitive chalogen ternary compounds of the formula X YZ where X denotes a member selected from the group consisting of Zn and Cd, Y a member selected from the group consisting of Si and Ge, and Z a member selected from the group consisting of S, Se and Te, or their solid solutions.

An object of this invention is to provide an electrophotographic photosensitive member having a sufliciently high sensitivity over the entire visible ray region.

Another object of this invention is to provide an electrophotographic photosensitive member which is particularly useful for color duplication.

A further object of this invention is to provide a method for imparting to conventional chalcogen ternary compounds a resistance suflicient to enable them to be used as materials for electrophotography by applying appropriate heat treatmente or chemical treatment to them.

Further objects and advantages of the present invention will be apparent from the following detailed description of the preferred embodiment thereof made with reference to the accompanying drawings in which:

FIG. 1 is an enlarged cross sectional view of a photo sensitive member embodying this invention;

FIG. 2 is a graph showing a relation between wavelength and relative photoconductivity of a photosensitive member embodying this invention; and

FIG. 3 is a graph showing a relation between wavelength and relative photoconductivity of a photosensitive member containing cadmium sulfide.

In this invention, a photosensitive member having preferable characteristics can be obtained in a case where two photosensitive layers containing the above-mentioned substances (I) and (II), respectively, are laminated on a base by laying, as a lower layer, a layer sensitive to long wavelength side, that is, layer 2 (in FIG. 1) containing cadmium chalcogen binary compounds, in close contact with the base plate 1 (in FIG. 1), and laying as the upper layer a layer sensitive to short wavelength side, that is, layer 3 (in FIG. 1) containing chalcogen ternary compounds. Although ,the thickness of each layer is not limited, it is preferable to select the thickness of the lower layer, which is made to make a close contact with the base, however 1 and 15011., preferably between 30 and 70 and that of the upper layer laid on the surface of the lower layer between 1 and 50 preferably between 1 and 1014.

A layer having a thickness of less than 1,11. is hard to manufacture and, when the thickness of the upper layer exceeds 50a, the rays are scattered before reaching the lower layer, and, as a result, unfavorable effect is caused. Moreover, since the sensitivity of photosensitive layer is reduced when it is too thick, the thickness of both upper and lower layer is limited of its own accord.

The examples of types chalcogen ternary compounds are as follows:

(a) Ternary compound containing Cd or Zn, Si or Ge,

' and chalcogen element, or mixture of the compounds.

(b) Solid solutions of the substances mentioned in (a).

() Solid solutions between the substances mentioned in (a) and cadmium (zinc) chalcogen binary compounds.

(d) Substances obtained by adding impurities such as Cu, Ag, and halogens to the substances mentioned in (a), (b), and (0) respectively.

(e) Various mixtures formed by combining the substances mentioned in (a), (b), (c), and (d).

The method for heat treatment or chemical treatment of chalcogen ternary compounds of this invention is as follows.

First the powder, 5 microns or more in grain diameter, of photoconductive chalcogen ternary compounds, obtained by mixing and fusing chalcogen ternary compounds, impurity, and flux is ground to fine powders, annealed at temperatures equal to the above-mentioned mix ing and fusing temperature or less for a long period of time to restore the photoconductivity and to obtain a sufficient resistance to be used as material for electrophotography.

When grinding the powder into fine grains 2 micron or less in diameter, the surfaces of the fine grains become very rough. Eifectiveness of grains is increased if the surfaces undergo dilute acid etching.

By these processings, disorders and defects of crystal latticev produced as the result of grinding are removed, the crystal surface is smoothened further, and the photoconductivity is considered to be recovered.

The chalcogen ternary compounds suitable for use in this invention may be synthesized directly by using the undermentionedsynthetic method. A mixture containing one or more of Cd or Zn chalcogenides and one or more simple substance of Ge or Si, or Ge or Si chalcogenide is combined in a ratio necessary to form chalcogen temary compounds such as Cd SiS Zn GeS etc. and the mixture is subjected to hydrothermal synthesis under a high vapor pressure. As general conditions of the synthesis, the temperature ranges from 280 to 400 (3., the pressure ranges from to 200 kg./cm. and the processing time ranges from 5 to 30 hours. The preferable conditions are temperatures lying within the range of 310 to 360 C., pressures within the range of to kg./cm. and processing time of 10 to 20 hours.

Furthermore the synthesis yield is increased when an adequate amount of chalcogen element is combined as a supplement material. Addition of activators such as Cu salts, Ag salts, and halogens can extend the sensitive wavelength region or increase its sensitivity.

Another method of synthesis to mix chalcogen compounds such as CdS, ZnS, and the like and chalcogen compounds such as Ge or Ge S, in a ratio adequate to form Cd GeS or Zn GeS add to the inixture about 10% by weight of halide such as cadmium chloride and the like as a flux and, if desired, add to the mixture an adequate amount of activator such as Cu salts, Ag salts, halogen and the like and pure water, mix them, and then dry to a rough powder.

When the rough powder is calcinated at a temperature higher than the melting point of the mixture (approximately 600 C., or higher) under atmospheric pressure, the above-mentioned photoconductive ternary compound is heat-synthesized in the form of a disintegrable block body. The calcination is desired to be performed in a stream of inert gas such as nitrogen gas, if possible.

Although this block body can be ground into photoconductive powder without any further treatment, if the block body is thrown into a deionized water, it crushes itself to be photoconductive powder having a grain diameter or approximately 10; and, at the same time, it is possible to remove the water soluble substances contained in the powder.

Some examples of preparation of the photosensitive ma terials, chalcogen compounds, are shown below. In the following examples, parts are by weight unless otherwise specified.

PREPARATION EXAMPLE 1 5776 parts of CdS powder, 281 parts of Si powder, and 640 parts of S and 50000 parts of distilled water were mlxed and introduced into a high-purity aluminum Tammann tube, and then the tube was placed in a stainless steel autoclave.

The autoclave was heated to a temperature of about 350 C., maintained at the temperature for about 15 hours, and then cooled. After cooled, the content of the Tammann tube was taken out, decanted, washed several times with pure water and dried to produce fine powders of a photoconductive ternary compound, Cd SiS having an averaged particle size of about 0.5,u.

1000 parts of fine powders of the resulting C(1 SiS compound and 2 parts of sulfur powders were introduced into a heat resistive glass test tube, subjected to heat treatment at 500 C. for 15 minutes in a nitrogen gas stream, calcinated for 15 minutes while evacuating with a rotary pump to remove excessive sulfur vapor, and cooled. The resulting product was subjected to classification by using pure water or alcohol to remove coarse particles, dried, and thereby there were obtained photoconductive fine powders for electrophotography having high dark resistance and comparatively uniform particle size.

PREPARATION EXAMPLE 2 Hydrogen sulfide gas was introduced into an aqueous strong hydrochloric acid solution obtained by dissolving GeO powder with HCl powder to precipitate white GeS The resulting precipitate was sufiiciently washed by decantation, filtered and dried. The GeS thus obtained (1366 parts) and 'CdS powder (5776 parts) were mixed with a flux, that is, 714 parts of CdCl and 71 parts of NH4C1, and further 2 parts of CuCl was added thereto as an activator. The mixture thus obtained was furthetr mixed with 2500 parts deionized water followedby-sufiicient kneading and drying.

The resulting dried blocks were ground to a desired particle size, placed in a quartz tube, and calcinated in a nitrogen gas stream at about 600 C. for 30 minutes. The product thus calcinated was put in a deionized water and spontaneously crushed to fine powders of about lO in size. The fine powders were repeatedly subjected to decantation and washing and then washed followed by drying. The resulting dry powders were placed in a quartz tube together with sulfur powder and calcinated in a nitrogen gas stream at about 500 C. for 15 minutes, and then excessive sulfur .vapor was evacuated by a rotary pump and the .content was cooled to give photoconductive powders suitable for electrophotographic materials.

In general, the chalcogen ternary compounds are bound with a resin to form a layer. In a similar way, the chalcogen binary compounds are also bound with a resin to form a layer.

A photosensitive member comprising a photosensitive layer according to this invention and an insulating layer provided on the surface of the photosensitive layer can give visible images of high contrast particularly by an electrophotographic method comprising applying a primary electric charge to the insulating layer on the photosensitive layer by corona discharging or electrode charging, applying a secondary electric charge having a polarity opposite to that of the primary charge or AC discharging, contemporaneously imagewise exposing to a radiant energy, if desired, applying a whole surface irradiation to form electrostatic latent images on the' insulating layer surface and developing by a Wet or dry developing method.

As binding resins used in this invention, there may be used those generally known as binding resins for electrophotography, for example, thermosetting resins such as epoxy resins, phenol resins, and unsaturated polyester resins, and thermoplastic resins such as polyvinyl chloride, polyvinylacetate, cellulose acetate, nitrocellulose, methacrylic resins, polyvinyl alcohol, polyvinyl butyral, and copolymer of vinyl chloride and vinyl acetate.

When laying an insulation layer on the photosensitive layer, such substances as polyester, polycarbonate, polyacetate, polystyrene, polyfiuoroethylene, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polyurethane, epoxy resin, and melamine resin may be coated on the photosensitive layer or pasted in a film form to the photosensitive layer to form an insulating layer.

The insulating layer so'made must possess insulating property, mechanical strength, elasticity, and transparency sufficient to meet the requirements. What is particularly important is that the insulating layer must be excellent in electrostatic charge holding property.

Moreover, the photosensitive member of this invention is not limited to have a photosensitive layer comprising two layers, that is, the upper layer and lower layer, but may have multilayer more than two layers by laying several additional layers. It is also possible to laminate, besides those mentioned above, other semiconductor layer, fluorescent layer, and the like.

As the support of the photosensitive member used in this invention, there may be used metal plates such as aluminum, copper, and zinc sheets, paper specially treated to prevent the solvent from permeating to the inside, plastic subjected to a conductive treatment, which are generally known as the support of photosensitive member for electrophotography.

This invention will be described more concretely by referring to the following examples. In the following examples, parts are by weight unless otherwise specified.

6 EXAMPLE 1 Parts (1) Commercially available photosensitive CdSpowder about 1/1. in grain diameter 50 (2) Photosensitive Cd SiS powder of about 11.1. in

grain diameter, produced by grinding Cd SiS obtained by heat synthesis in a ball mill for two days, annealing the Cd SiS for about 10 hours at about 700 C., sieving the annealed Cd SiS by using a deionized water to remove coarse powder and extremely fine powder, and drying 50 To each of the above-mentioned photosensitive substance powders (1) and (2) were added 10 parts of vinyl chloride-vinyl acetate copolymer resin and, as solvent of the resin, an adequate amount of thinner. After complete mixing, the mixtures were subjected to roll mill to improve dispersion, and thus pasty mixtures were prepared.

First, the pasty mixture containing the photosensitive substance of (1) above was spread uniformly over an aluminum foil using an appropriate spacer and an appropriate blade in such a way that the thickness of the coat Was about 40 after dry. The aluminum foil was left to stand for several hours to dry and then was heated to dry for 2 hours at 60 C. Next, to the dried surface was applied a coat of pasty mixture containing the photosensitive substance of (2) as mentioned above in a similar way to the above so that the dry thickness was about 10 and the layer was dried. Thus an electrophotographic photosensitive member was obtained.

The spectral characteristics of photoconductivity were measured by vapor-depositing aluminum electrodes, 5 mm. in Width and 0.5 mm. in spacing, on the surface of photosensitive layer of the photosensitive member. The result shows sufficient sensitivity over the entire region of visible light as shown in 'FIG. 2. With respect to abscissa and ordinate of graphs in FIG. 2 and FIG. 3, a photosensitive layer is formed between metal electrodes of 5 mm. in width and 0.5 mm. in spacing and a voltage of about v. is applied thereto and then a monochrornic light having a known intensity obtained through a spectrograph is projected to the photosensitive layer. Various monochromic light are successively projected thereto. The resulting photo-current between the electrodes is determined by an ampere meter. The photo-current value is adjusted depending on spectral intensity distribution of the projected light and further normalized by assuming the peak value as 1. This is relative photoconductivity on the ordinate, and, the ordinate corresponds to wavelength of the projected light.

Splendid color reproducibility was displayed in the tri-color duplication using filters. Kodak Wratten filters No. 25 (red), No. 58 (green), and No. 47B (blue) for tri-color resolution were prepared, and as color developers, colored powder positive toners of three colors, cyan, magenta, and yellow, were also prepared.

These color developers can be obtained easily by only replacing, in the ordinary black toner colored by carbon black, the coloring agent, i.e. carbon black, by cyan, magenta, and yellow coloring matters, for example, Methylene Blue, Fuchsine, and Oramin.

Next, the surface of the above-mentioned photosensitive member was subjected to uniform negative charging in a dark place. Then light irradiation from an original image which is illuminated by white light source is applied to the surface through Wratten filter N0. 25. The electrostatic image obtained by eliminating the surface charge selectively was developed by a cyan color positive toner. The toner image was bias transferred onto a white copying paper. The image was fixed and the surface of the photosensitive member was cleaned.

The same operation was repeated for the combination of Wratten filter No. 5 8 and magenta color toner and the combination of Wratten filter No. 47B and yellow color toner.

The same copying paper was used each time and attention was paid not to displace the position of the copying paper at each time.

The exposure time was about A second for each time and the intensity of illumination of total illuminated rays of light on the photosensitive member was about 178 lux. Thus an excellent colored image was reproduced.

EXAMPLE 2 Parts (1) Commercially available CdS powder about 1,1

in grain diameter 50 (2) Photosensitive Cd SiS powder of about 1 in grain diameter obtained by grinding, Cd SiS produced by heat synthesis in a ball mill for two days, by annealing then for about 10 hours at about 700 C., classifying the annealed Cd SiS with a deionized water to remove rough powder and extremely fine powder and drying 50 (3) Vinyl chloride-vinyl acetate copolymer resin 10 (4) Thinner as a solvent for the resin of (3) above appropriate amount The combination of ingredients (1) through (4) mentioned above was thoroughly mixed and subjected to a roll mill treatment in order to further improve dispersion. The mixture was then spread smoothly on the aluminum foil by using a spacer and a blade, dried for several hours, and then subjected to heat drying for 2 hours at 60 C. Thus an electrophotographic photosensitive member was obtained.

The spectral characteristic of photoconductivity was measured by vapor-depositing two aluminum electrodes, 5 mm. in width and spaced by 0.5 mm. The photosensitive layer had a sufiicient sensitivity to the entire visible light region.

The photosensitive member had a splendid color reproduction in tri-color duplication using three filters as in Example 1.

EXAMPLE 3 Two pasty mixtures were prepared by adding to each of the photosensitive substances (1) and (2) used in Example 1 parts of a vinyl chloride-vinyl acetate copolymer resin and an adequate amount of thinner as solvent, throughly mixing them, and grinding the mixtures in a roll mill to improve dispersion. First, the pasty mixture containing the photosensitive substance of (1) above was spread smoothly on an aluminum foil by using an appropriate spacer and a blade in such a way that the thickness of the layer was about 40 after drying. The foil was then left to stand for several hours to dry itself, then heated and dried for two hours at 60 C.

Next, the pasty mixture containing the photosensitive substance (2) above was spread on the surface in similar manner to the above so that the thickness after drying was about 10;!" The mixture was dried and an electrophotographic photosensitive member having two layers was obtained.

On the surface of the photosensitive layer of the photosensitive member was vapor-deposited aluminum electrodes in a manner similar to Example 1 and the spectral characteristics were measured. Spectral sensitivity to entire visible ray region as shown in FIG. 2 was shown similar to the photosensitive member of Example 1.

In this case the photosensitive layer is not limited to comprise two layers, an upper layer and a lower layer, but may comprise multiple layers laminated more than two layers.

EXAMPLE 4 On a smooth surface of an aluminum sheet, a photoconductive CdS powder layer bound with a resin of about 50,11. in thickness was formed and fixed by using about by weight of epoxy resin as a binder. Further thereon, a layer of about 5 in thickness and bound by an epoxy resin was formed and fixed as before.

This layer contained a mixture of Cd GeS and Zn GeSe obtained by heat synthesis in a weight ratio of 5:1. These photoconductive powders were prepared by grinding blocks of Cd GeS and Zn GeSe agitating vigorously in a large amount of water While adding a small amount of hydrochloric acid dropwise to smoothen the surface of the ground particles, repeating decantation and washing, simultaneously classifying, drying and annealing at 600 C. for 5 hours.

The resulting photosensitive plate was also panchromatic and of high sensitivity in a Way similar to Example 1.

Further, in a way similar to Example 1, the resulting photosensitive plate gave excellent reproduction of color in a tri-color duplication using filters.

EXAMPLE 5 A chargeable member was obtained by laminating a transparent fluorine containing resin film or polyester film of about 15,11. in thickness to a photosensitive member obtained in similar manner to Example 1 by using an epoxy resin binder. Next, to the surface of the fluorine containing resin film of the above-mentioned chargeable member was applied +6 kv. corona discharge to have the surface charged uniformly with positive charge. Then, an original image was projected to the above-mentioned surface by a tungsten lamp of about 10 lux and simultaneously AC corona discharge of 6 kv. was applied to the same surface. Further, the entire area of previously mentioned surface was subjected to a uniform exposure for 12 seconds from a 10 w. tungsten lamp to form an electrostatic latent image that conform to the bright-dark pattern of the original image. Next, the electrostatic image was developed by a magnet brush method. A fogless, good quality visible image having a high image density was obtained. In a tri-color duplication using filters similar to Example 1, reproduction of colors was excellent.

What is claimed is:

1. An electrophotographic photosensitive member which comprises a photoconductive layer composed of a photoconductive CdS and finely divided particles of a member selected from the group consisting of Cd SiS Cd SiSe C(14SlTe Cd GQSG, C(1 GeSe Cd4GeTe Zn 'SiS ZII Sl'SE Zn SiTe ZH GfiS ZH4GS6 and Zn GeTe said finely divided member having been annealed at a temperature of about 500-700 C. to recover the photoconductivity, wherein the CdS and said member are dispersed in a binder resin at about equivalent ratio.

2. An electrophotographic photosensitive member according to claim 1 in which an insulating layer is provided on the photosensitive layer.

3. An electrophotographic photosensitive member according to claim 2 in which a material of the insulating layer is a member selected from the group consisting of polyester, polycarbonate, polyacetate, polystyrene, polyfiuoroethylene, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polyurethane, epoxy resin and melamine resin.

References Cited UNITED STATES PATENTS 3,492,620 1/1970 Kaldis et al. 252-501 X 3,174,939 3/1965 'Suchow 252-501 3,104,229 9/1963 Koelmans et al. 252-501 GEORGE F. LESMES, Primary Examiner J. R. MILLER, Assistant Examiner US. Cl. X.R. 252-50l; 96-12. 

